Pediatric health service differs between and within countries. To prioritize limited resources, data-driven studies on pediatric tertiary hospital contacts are warranted. This population-based register study identified all contacts with four Danish tertiary hospitals 2000–2018 by 0–17-year-old patients. During 2000–2018, 2,496,001 individuals resided in Denmark while 0–17 years old, and the study described 829,562 inpatient and 3,932,744 outpatient contacts at tertiary hospitals by hospital, sex, age, diagnosis, department, and residence. Male patients accounted for more contacts overall (inpatient 55.51%, outpatient 52.40%) and more contacts with severe chronic disease (inpatient 56.24%, outpatient 54.41%). Median (interquartile range) patient age was 3.09 (0.26–9.96) and 8.48 (2.78–13.70) years for in- and outpatient contacts. Overall, 28.23% and 21.02% of in- and outpatient contacts included a diagnosis of a severe chronic disease, but the proportions differed across hospitals. A pattern of pediatric healthcare directed towards less severe diseases was observed: While the total number of outpatient visits at tertiary hospitals increased from 2000 to 2018, the proportion of these contacts which had a diagnosis of a severe chronic disease decreased. Future comparisons between hospitals regarding pediatric outcomes should consider potential differences in terms of uptake and diagnosis severity. Such findings may have implications for future pediatric organization, nationally and internationally.